Method for preparing aromatic diphenyl thioethers

ABSTRACT

The invention concerns a method for preparing aromatic diphenyl thioethers. More particularly the invention concerns the preparation of 4-chloro-4′-thiomethyldiphenylether. The inventive method for preparing an aromatic diphenyl thioether is characterised in that it consists in reacting in an aqueous medium a diazonium salt of an aromatic diphenyl compound with a disulphide sulphur compound, in the presence of an efficient amount of a coupling catalyst.

This application is an application under 35 U.S.C. Section 371 ofInternational Application Number PCT/FR99/03273 filed on Dec. 23, 1999.

The present invention relates to a process for preparing biphenyl typearomatic thioethers.

More precisely, the invention relates to the preparation of an aromaticcompound comprising a concatenation of at least two phenyl groups atleast one of which carries a thioether group.

More particularly, the invention relates to the preparation of4-chloro-4′-thiomethyldiphenyether.

When a functional group is to be introduced into a biphenyl typemolecule, there is a problem with introducing a functional group intoonly one of the benzene rings.

The present invention aims to provide a process that consists ofintroducing at least one thioether group into one of the phenyl groups.

It has now been discovered, and this forms the subject matter of thepresent invention, a process for preparing a biphenyl type aromaticthioether, characterized in that a diazonium salt of a biphenyl typearomatic compound is reacted with a disulphide type sulphur-containingcompound in an aqueous medium in the presence of an effective quantityof a coupling catalyst.

The term “biphenyl type aromatic thioether” means a concatenation of twophenyl groups connected together wherein at least one of the benzenerings carries a thioether function.

In a preferred variation of the process of the invention, the thioetheris prepared using a process that associates preparation of the diazoniumsalt from the corresponding aromatic amine then, without separation,carrying out the reaction with the sulphur-containing compound.

In accordance with the process of the invention, a biphenyl typearomatic amine can be used as the starting compound; in a first step, itis transformed into a diazonium salt.

The term “biphenyl type aromatic amine” means a concatenation of twophenyl groups connected together wherein at least one of the benzenerings carries an amine function.

The starting aromatic amine can be represented by the following generalformula (1):

in which formula (I):

R₁ represents a hydrogen atom or a substituent R;

Z represents:

a covalent bond;

an alkylene or alkylidene group containing 1 to 4 carbon atoms,preferably a methylene or isopropylidene group;

a group B which may be one of the following atoms or groups:

—O—, —CO—, —COO—, —OCOO—

—S—, —SO—, —SO₂—,

 in which formulae, R₂ represents a hydrogen atom or an alkyl groupcontaining 1 to 6 carbon atoms, or a phenyl group.

In formula (I), one or both benzene rings can be substituted, meaningthat in the biphenyl type starting substrate, at least one of the 5hydrogen atoms of the aromatic ring can be replaced by an atom otherthan a hydrogen atom. In particular, it can be a halogen atom, carbon,oxygen or nitrogen.

Group R₁ represents a hydrogen atom or any other group R.

Group R can have any nature provided that it does not interfere with thediazotisation reaction.

Non-limiting examples of substituents that can be cited are given below:

a linear or branched alkyl group, preferably containing 1 to 6 carbonatoms, more preferably 1 to 4 carbon atoms;

a linear or branched alkenyl group preferably containing 2 to 6 carbonatoms, more preferably 2 to 4 carbon atoms;

a linear or branched halogenoalkyl group preferably containing 1 to 4carbon atoms, and 1 to 9 halogen atoms;

a cycloalkyl group containing 3 to 7 carbon atoms, preferably acyclohexyl group;

a phenyl group;

a hydroxyl group;

a NO₂group;

a R₃—O— alkoxy group or R₃—S— thioether group where R₃ represents alinear or branched alkyl group containing 1 to 6 carbon atoms,preferably 1 to 4 carbon atoms, or a phenyl group;

a —N—(R₂)₂ group where groups R₂, which may be identical or different,represent a hydrogen atom, a linear or branched alkyl group containing 1to 6 carbon atoms, preferably 1 to 4 carbon atoms, or a phenyl group;

a —NH—CO—R₂ group where R₂ has the meaning given above;

a carboxyl group or R₂—O—CO— derivative, where group R₂ has the meaninggiven above;

an acyloxy or aroyloxy group R₃—CO—O—, where group R₃ has the meaninggiven above;

a B(OR₃)₂ group, where group R₃ has the meaning given above;

a halogen atom, preferably a fluorine atom;

a CF₃ group;

two groups R can together form an alkylenedioxy group containing 1 to 4atoms in the alkylene group, preferably a methylenedioxy orethylenedioxy group.

Preferred groups R that can be cited are a halogen atom, preferably afluorine, chlorine or bromine atom or a halogenoalkyl group, preferablyperfluoroalkyl; a hydroxyl group; an alkyl or alkoxy group containing 1to 6 carbon atoms, preferably 1 to 4 carbon atoms; an amino group or anamino group substituted with one or two alkyl groups containing 1 to 6carbon atoms, preferably 1 to 4 carbon atoms.

Preferred compounds are those with formula (I) where R₁ represents afluorine atom or a chlorine atom and Z represents an oxygen atom.

In accordance with the process of the invention, in a first step thediazonium salt of the biphenyl type aromatic amine preferably withformula (I) is prepared.

To this end, to transform the amino group into a diazonium group, thestarting substrate is reacted with an acid. While it is possible to usean acid such as sulphuric acid, it is preferable to use a hydrogen acidto put the amine group into the halohydrate salt form.

Thus, the starting substrate preferably with formula (I) is preferablyreacted with hydrochloric acid or hydrobromic acid.

The quantity of acid used is such that the mole ratio between the numberof H⁺ ions and the number of moles of substrate is in the range 2.0 to2.5, preferably in the range 2.0 to 2.2.

In the next step, the diazonium salt is prepared by reacting thebiphenyl type aromatic amine in the halohydrate form with adiazotisation reactant that is any source of NO+.

Thus it is possible to start from nitrogen dioxide NO₂, nitrogentrioxide N₂O₃, nitrogen tetroxide N₂O₄, nitric oxide NO associated withan oxidising agent such as nitric acid, nitrogen dioxide or oxygen. Whenthe reactant is a gas under the reaction conditions, it is bubbled intothe mediun.

It is also possible to use a nitrous acid, a nitrosyl sulphide or anitrose or a nitrous salt, preferably an alkali metal salt, morepreferably a sodium salt.

It is also possible to use alkyl nitrites, more particularly those withformula (II):

R_(a)—ONO  (II)

in which formula (II), R_(a) represents a linear or branched alkyl groupcontaining 1 to 12 carbon atoms, preferably 1 to 4 carbon atoms.

Advantageously, sodium nitrite is used.

The quantity of diazotisation reactant used can vary widely. When it isexpressed as the mole ratio of the aromatic aminel diazotisationreactant defined as NO⁺, it is at least equal to the stoichiometricquantity but preferably, it is used in an excess of up to 120% of thestoichiometric quantity, preferably in the range 100% to 120%.

Regarding the concentration of the aromatic amine substrate in thereaction medium, it is preferably in the range 0.5 to 2.5 mol/l, morepreferably about 1 mol/l.

The amine halohydrate is prepared by simply mixing the starting amineand the acid.

The reaction is advantageously carried out at a temperature in the range50° C. to 100° C.

The diazotisation reactant is then added, preferably slowly in fractionsor continuously.

Regarding the temperature of the diazotisation reaction, this isgenerally a low temperature, advantageously in the range −10° C. to 20°C., preferably in the range 0° C. to 10° C.

In the process of the invention, the sulphur-containing compound isreacted with the diazonium salt obtained, which preferably has thefollowing formula (III):

in which formula (III):

X represents a halogen atom X, preferably a chlorine or bromine atom, aHSO₄ ⁻ group or a SO₄ ⁼ group;

R₁ and Z have the meanings given above;

n equals 1 or 2.

The sulphur-containing compound used preferably has the followingformula (IV):

R₄—S—S—R₅  (IV)

in said formula (IV):

R₄ and R₅, which may be identical or different, represent a hydrocarbongroup containing 1 to 24 carbon atoms, which can be a saturated orunsaturated, linear or branched aliphatic acyclic group; a saturated,unsaturated or aromatic, monocyclic or polycyclic carbocyclic orheterocyclic group, or a linear or branched, saturated or unsaturatedaliphatic group carrying a cyclic substituent.

The sulphur-containing compound used in the process of the invention hasformula (IV) where R₄ and R₅ can have a number of meanings. Different,non-limiting, examples will be given below.

With compounds with formula (IV), R₄ and R₅ preferably represent asaturated or unsaturated, linear or branched acyclic aliphatic grouppreferably containing 1 to 24 carbon atoms, comprising one or moreunsaturated bonds in the chain, generally 1 to 3 unsaturated bonds whichmay be simple double bonds or conjugated double bonds or triple bonds.

More particularly, R₄ and R₅ represent a linear or branched alkyl,alkenyl, or alkadienyl group preferably containing 1 to 12 carbon atoms.

R₄ and R₅ represent a linear or branched halogenoalkyl group preferablycontaining 1 to 12 carbon atoms, more preferably 1 to 4 carbon atoms,and 3 to 25 halogen atoms.

The hydrocarbon chain can optionally be:

interrupted by a functional atom or group; groups B cited above may becited in this respect;

and/or carry the following substituents:

—OH, —COR₃, —COOR₂, —CHO, —CN, —NO₂, —CF₃,

where R₂, which may be identical or different, and R₃ have the meaninggiven above.

Groups R₄ and R₅ can represent a halogenoalkyl group, preferablyperhalogenoalkyl, or a halogenoalkenyl group.

In formula (IV), the saturated or unsaturated linear or branchedaliphatic acyclic group can optionally carry a cyclic substituent. Theterm “cycle” means a saturated, unsaturated or aromatic carbocyclic orheterocyclic cycle.

The aliphatic acyclic group can be bonded to the cycle by a covalentbond or by a group B as cited above.

Examples of cyclic substituents that can be envisaged arecycloaliphatic, aromatic or heterocyclic substituents, in particularcycloaliphatic substituents containing 6 carbon atoms in the cycle orbenzenic substituents, such cyclic substituents themselves optionallycarrying one or more substituents.

Examples of such groups that can be mentioned are the benzyl group.

In general formula (IV), R₄ and R₅ can represent a monocycliccarbocyclic group. The number of carbon atoms in the cycle can varywidely from 3 to 8 carbon atoms, but is preferably 5 or 6 carbon atoms.

The carbocyle can be saturated or may comprise 1 or 2 unsaturated bondsin the cycle, preferably 1 or 2 double bonds.

Preferred examples of groups R₄ and R₅ that can be cited are cyclohexylor cyclohexeneyl groups.

When R₄ or R₅ represents a saturated or unsaturated monocycliccarbocyclic group, one or more of the carbon atoms of the cycle may bereplaced by a heteroatom, preferably oxygen, nitrogen or sulphur or by afimctional group, preferably carbonyl or ester, leading to a monocyclicheterocyclic compound. The number of atoms in the cycle can be in therange 3 to 8 atoms, preferably 5 or 6 atoms.

Groups R₄ and R₅ can also be polycyclic carbocyclic, preferablybicyclic, meaning that at least two cycles have two carbon atoms incommon. With polycyclic groups, the number of carbon atoms in each cycleis in the range 3 to 6: the total number of carbon atoms is preferably 7.

Groups R₄ and R₅ can also be polycyclic heterocyclic, preferablybicyclic, which means that at least two cycles have two atoms in common.In this case, the number of atoms in each cycle is in the range 3 to 6,more preferably 5 or 6.

Groups R₄ and R₅ preferably represent an aromatic carbocyclic group, inparticular benzenic or a concatenation of 2 or 3 benzene rings separatedby atoms or groups B as defined above.

Examples of groups R₄ and R₅ with formula (IV) that can moreparticularly be mentioned are phenyl groups.

R₄ and R₅ can also represent a polycyclic aromatic hydrocarbon group;the cycles can between them form ortho-condensed or ortho- andperi-condensed systems. More particularly, the group can be the naphthylgroup.

In general formula (IV), R₄ and R₅ can also represent an aromaticheterocyclic group in particular comprising 5 or 6 atoms in the cycle,wherein 1 or 2 are heteroatoms such as nitrogen, sulphur or oxygen.

Illustrative examples of heterocyclic groups that can be cited aretetrahydrofuryl, tetrahydrothienyl, pyrrolidinyl, furyl, thienyl,pyrrolyl and pyridyl.

R₄ and R₅ can also represent a polycyclic aromatic heterocyclic groupdefined as either a group constituted by at least two aromatic or nonaromatic heterocycles containing at least one heteroatom in each cycleand forming between them ortho- or ortho- and peri-condensed systems, ora group constituted by at least one aromatic or non aromatic hydrocarboncycle and at least one aromatic or non aromatic heterocycle formingbetween them ortho- or ortho- and peri-condensed systems.

Illustrative examples of polycylic groups that can be cited are:isoquinolyl, quinolyl, naphthyridinyl, benzofuranyl and indolyl.

It should be noted that if group R₄ and R₅ comprises a cycle, that cyclemay carry a substituent. The nature of the substituent is irrelevant aslong as it does not interfere with the desired product. The substituentsare of the same nature as R.

Preferred examples of groups R₄, R₅ that can be cited are linear orbranched alkyl groups containing 1 to 4 carbon atoms, 2-carboxyethyl,cyclohexyl, phenyl, benzyl, benzoyl, pyridyl, etc.

The process is readily carried out using a number of sulphur-containingcompounds.

Preferred examples of disulphide type sulphur-containing compounds thatcan be mentioned are:

dimethyldisulphide;

diethyldisulphide;

di-n-propyldisulphide;

diisopropyldisulphide;

di-n-butyldisulphide;

diisobutyldisulphide;

di-sec-butyldisulphide;

di-tert-butyldisulphide;

diisoamyldisulphide;

di-n-hexyldisulphide;

di-tert-heptyldisulphide;

di-n-undecyldisulphide;

distearyldisulphide;

diallyldisulphide;

dicyclohexyldisulphide;

diphenyldisulphide;

dibenzyldisulphide

dibenzoyldisulphide;

dithiopyridine;

dithioglycolic acid.

Preferred compounds from the list cited above are dialkyldisulphidespreferably containing 1 to 4 carbon atoms in the alkyl portion.

The quantity of sulphur-containing compound is such that said mole ratiois preferably in the range 1 to 1.5.

The coupling reaction is carried out in an aqueous medium. The quantityof water present in the reaction medium generally represents 100% to500% by weight of the aromatic amine.

In a variation, the process of the invention consists of adding anorganic solvent which is inert under the reaction conditions.

Examples of organic solvents that can be cited are saturated aliphaticmonocarboxylic acids, more particularly formic acid, acetic acid,propionic acid, butyric acid, isobutyric acid, pentanoic acid and2-methylbutanoic acid.

Acetic acid is the preferred saturated aliphatic monocarboxylic acid.

It is also possible to use a solvent such as acetone ordimethylformamide.

The quantity of organic solvent used, expressed as the weight ofstarting amine, is advantageously in the range 100% to 1000%, preferablyin the range 200% to 500%.

In the process of the invention, the diazonium salt, preferably withformula (III), is reacted with the sulphur-containing compound,preferably with formula (IV): the reaction is carried out in thepresence of a coupling catalyst.

The coupling catalyst is a catalyst comprising at least one metallicelement selected from the 4^(th) and 5^(th) period of groups IIIA, IVA,VA, VIA, VIIA, VIII, IB and IIB of the periodic table.

Preferred metals that can be cited are: copper, iron, cobalt, nickel,palladium and platinum.

The elements are defined in the periodic table published in the“Bulletin de la SociétéChimique de France, No.1 (1966).

The metallic elements can also be supplied in the form of a zero metalor an inorganic derivative such as an oxide or hydroxide. It is possibleto use a mineral salt, preferably a nitrate, sulphate, oxysulphate,halide, oxyhalide, silicate, carbonate or an organic derivative,preferably a cyanide, oxalate, acetylacetonate; an alcoholate, morepreferably a methylate or ethylate; or a carboxylate, more preferably anacetate. It is also possible to use complexes, in particularchlorine-containing or cyanide-containing complexes of said metalsand/or alkali metals, preferably sodium or potassium, or ammonium.

More specific examples of palladium catalysts that can be cited arepalladium (II) chloride, hydrated palladium (II) nitrate, dihydratedpalladium (II) sulphate, palladium (II) acetate, ammoniumtetrachloropalladate (II), potassium hexachloropalladate (IV), andpalladium (II) tetrakisphenylphosphine.

Platinum catalysts that can be mentioned include platinum (II) chloride,ammonium tetrachlorplatinate (II), ammonium hexachloroplatinate (IV),hydrated sodium tetrachloroplatinate (IV), hexahydrated sodiumhexachloroplatinate (IV), potassium hexachloroplatinate (IV), andhexahydrated chloroplatinic acid.

Nickel or cobalt catalysts that can be cited include nickel (II) bromideand chloride and cobalt (II) chloride or bromide.

The catalyst of choice used in the process of the invention iscopper-based.

Examples of catalysts that can be cited are copper metal or organic orinorganic copper I or copper II compounds.

Preferably, catalysts based on copper 0 and I are used.

Non limiting examples of copper compounds that can be cited are cuprousbromide, cupric bromide, cuprous iodide, cuprous chloride, cupricchloride, basic copper II carbonate, cuprous nitrate, cupric nitrate,cuprous sulphate, cupric sulphate, cuprous sulphite, cuprous oxide,cuprous acetate, cupric acetate, cupric trifluoromethylsulphonate,cupric hydroxide, copper I methylate, copper II methylate, andchlorocupric methylate with formula ClCuOCH₃.

The quantity of catalyst used, expressed as the ratio of the weight ofdiazonium salt is generally in the range 0.1 to 20 mole %, preferably 1%to 10%.

The coupling reaction between the diazonium salt preferably with formula(III) and the sulphur-containing compound is advantageously carried outat a temperature in the range 0° C. to 120° C., preferably in the range80° C. to 100° C.

In general, the reaction is carried out at atmospheric pressure, butlower or higher pressures may also be suitable. Autogenous pressure isemployed when the reaction temperature is higher than the boilingtemperature of the reactants and/or products.

In a preferred variation of the process of the invention, the process ofthe invention is carried out in a controlled atmosphere of inert gas. Arare gas atmosphere can be established, preferably argon, but nitrogenis more economical.

The reaction is continued until the diazonium salt is completelytransformed. The reaction progress can be monitored using anyconventional analytical technique such as gas chromatography or highperformance liquid chromatography.

The reaction period is generally short, of the order of 30 min to 2hours.

From a practical viewpoint, the two reactants are brought together inany order. In a preferred variation, the sulphur-containing compound ispreferably added to the diazonium salt, followed by the catalyst.

At the end of the reaction, two phases are obtained; the aqueous phasecomprises all of the salts formed and the organic phase comprises, inaddition to any excess reactants, the desired compound which preferablyhas formula (VI):

in which formula (VI), R₁, R₄ and Z have the meanings given above.

The desired product is recovered from the organic phase usingconventional techniques. By way of illustration, it is possible to addan organic solvent, for example isopropyl ether or an alkane such asmethylcyclohexane, to extract all of the organic compounds and then,from this organic phase, to separate the compound using the usualseparation techniques such as distillation or crystallisation from asuitable solvent, preferably an alcohol, more particularly methanol orisopropanol.

The following examples are given by way of illustration and are in noway limiting in nature.

The following abbreviations are used in the examples:

TT=number of moles of 4-chloro-4′aminodiiphenylether transformed,/numberof moles of 4-chloro-4′aminodiphenylether introduced%

 RR=number of moles of 4-chloro-4′thiomethyldiphenylether formed,/Number of moles of 4-chloro-4′aminodiphenylether introduced%

EXAMPLE 1

2.20 g (10 mmoles) of 4-chloro-4′-aminodiphenylether, 8 ml of water and,with stirring, 2.33 g (23 mmoles) of 36% hydrochloric acid were chargedinto a 50 ml double envelope reactor.

It was heated to 90° C. and the mixture became homogeneous.

This temperature was maintained for 45 minutes then it was cooled to 10°C.

0.69 g (10 mmoles) of an aqueous 30% sodium nitrite solution was pouredin over two hours using a syringe driver.

The diazonium salt was added dropwise to a mixture of 0.82 g ofdimethyldisulphide and 5 ml of water and 31 mg of copper metal in a 100ml reactor at 50° C.

15 ml of isopropyl ether was added.

The reactor was emptied and the organic phase was washed with 100 ml ofwater and 100 ml of 10% sodium bisulphite in water and again with 100 mlof water.

The organic phase was concentrated under reduced pressure of 2 mbars, at50° C. for 1 hour.

1.38 g of 4-chloro4′-thiomethyldiphenylether was obtained, correspondingto a degree of transformation of 100% and a yield RR of 55%.

The product obtained could be purified by crystallisation from methanol.

EXAMPLES 2 TO 14

The above example was repeated, changing the nature of the catalyst.

The quantity of product formed was determined by gas chromatographicanalysis.

The results are shown in Table (I).

TABLE (I) Ex. Ref Nature of catalyst Yield 2 CuBr₂ 63.0% 3 CuSO₄ 62.7% 4CuCl₂,2H₂O 61.2% 5 CuBr 48.9% 6 Cu₂O 37.3% 7 Pd(AcO)₂ 26.6% 8 Pd(PPh₃)₄25.5% 9 NiBr₂ 24.6% 10 PdCl₂ 24.4% 11 CoCl₂,6H₂O 20.2% 12 Pd/C 18.9% 13MnCl₂ 14.4% 14 AgNO₃ 10.9%

EXAMPLE 15

165 g of Cl—Ph—O—Ph—NH₂ (0.75 moles) was charged into a 2.0 litrethree-necked flask provided with a thermometer, a dropping funnel, acoolant surmounted by an argon reservoir (balloon) and maintained underan inert atmosphere with vigorous magnetic stirring. 300 ml of aceticacid was then added.

The assembly was heated to 80° C. then 82.5 g of a concentrated aqueoushydrochloric acid solution (37%) was slowly added.

The reaction medium was stirred for about 45 min at 80° C.

The temperature was allowed to return to 65° C. with stirring.

213 g of CuCl₂ was then added to the reaction medium, followed by 132 mlof Me₂S₂.

Then an aqueous NaNO₂ solution (solution of 54 g in 120 ml of H₂O) wasadded using the dropping funnel.

When no more gas had been released, the temperature was returned toambient temperature and the medium was diluted with 360 ml of water. Twophases appeared.

500 ml of methycyclohexane was added and the two phases were separated.

The aqueous phase was extracted again with methylcyclohexane (500 ml).

After evaporating off the methylcyclohexane, 242 g of a brown oil wasrecovered. The crude product was recrystallised to produce 124 g ofpink-white crystals (yield: 66%; purity: 97.2%, determined by gaschromatography; and MPt=56.0° C.).

A second recrystallisation was possible.

What is claimed is:
 1. A process for preparing a biphenyl aromaticthioether compound, comprising the step of reacting a diazonium salt ofa biphenyl aromatic compound with a disulphide compound, in an aqueousmedium, and in the presence of a catalyzing effective amount of acoupling catalyst.
 2. A process according to claim 1, comprising thefollowing steps: 1) preparing the diazonium salt from a biphenylaromatic amine compound, then, without separation, 2) reacting with thediazonium salt with the disulphide compound.
 3. A process according toclaim 2, wherein the biphenyl aromatic amine compound has the followingformula (I)

wherein R₁ is a hydrogen atom or a substituent R which does notinterfere with the diazonium salt reaction, and Z is: a covalent bond,an alkylene or alkylidene group having 1 to 4 carbon atoms, or a groupor atom B selected from the group consisting in the groups or atoms ofthe following formula: —O—, —CO—, —COO—, —OOC—, —OCOO—, —S—, —SO—,—SO₂—,

 wherein R₂ is a hydrogen atom, an alkyl group having 1 to 6 carbonatoms, or a phenyl group.
 4. A process according to claim 3, wherein Z amethylene group or an isopropylidene group.
 5. A process according toclaim 3, wherein R is: a linear or branched alkyl group, a linear orbranched alkenyl group, a linear or branched halogenoalkyl group, acycloalkyl group having 3 to 7 carbon atoms, a phenyl group, a hydroxylgroup, a NO₂ group, a R₃-O— alkoxy group or a R₃—S— thioether groupwherein R₃ is a linear or branched alkyl group having 1 to 6 carbonatoms, a —N—(R2)₂ group wherein R₂, which is identical or different, isa hydrogen atom, or a linear or branched alkyl group having 1 to 6carbon atoms, a —NH—CO—R₂ group wherein R₂ is a hydrogen atom, or alinear or branched alkyl group having 1 to 6 carbon atoms, a carboxylgroup or a R₂—O—CO— group, wherein R2 is a hydrogen atom, or a linear orbranched alkyl group having 1 to 6 carbon atoms, an acyloxy or aroyloxygroup R₃—O—O—, wherein R₃ is a linear or branched alkyl group having 1to 6 carbon atoms, a B(OR₃)₂ group, wherein R₃ is a linear or branchedalkyl group having 1 to 6 carbon atoms, or a CF₃ group.
 6. A processaccording to claim 5, wherein R is a methylenedioxy group or anethylenedioxy group.
 7. A process according to claim 2, wherein step 1)comprises the preparation of the dfazonium salt of the biphenyl aromaticamine by reacting said amine with a hydrogen acid and a diawotisationsource of NO⁺.
 8. A process according to claim 7, wherein the hydrogenacid is hydrochloric acid or hydrobromic acid.
 9. A process according toclaim 7, the number of H⁺ ions of the acid and the number of moles ofthe amine is in a molar ratio in the range from 2.0 to 2.5.
 10. Aprocess according to claim 9, wherein the mole ratio is in the rangefrom 2.0 to 2.2.
 11. A process according to claim 7, wherein thereaction between the biphenyl aromatic amine and the hydrogen acid iscarried out at a temperature in the range from 50° C. to 100° C.
 12. Aprocess according to claim 7, wherein the source of NO⁺ is a NO, NO₂,N₂O₃, N₂O₄, associated with an oxidising agent.
 13. A process accordingto claim 3, wherein the diazonium salt has the following formula (III):

wherein: X is a halogen atom, a HSO₄ ⁻ group, or a SO₄ ⁼ group, n is 1or 2, R₁ is a hydrogen atom or a substituent R which does not interferewith the diazonium salt reaction, and Z is: a covalent bond, an alkyleneor alkylUdene group containing 1 to 4 carbon atoms, or a group or atom Bselected from the group consing in the groups or atoms of the followingformula: —O—, —CO—, —COO—, —OOC—, —OCOO—, —S—, —SO—, —SO₂—,

 wherein R₂ is a hydrogen atom, an alkyl group having 1 to 6 carbonatoms, or a phenyl group.
 14. A process according to claim 1, whereinthe disulphide compound has the following formula (IV): R₄—S—S—R₅  (IV)wherein R₄ and R₅, which are identical or different, are hydrocarbongroups having 1 to 24 carbon atoms.
 15. A process according to claim 14,wherein R₄ and R₅, which are identical or different, are saturated orunsaturated, linear or branched, acyclic aliphatic groups.
 16. A processaccording to claim 14, wherein R₄ and R₅, which are identical ordifferent, are saturated, unsaturated or aromatic, monocyclic orpolycyclic, carbocyclic groups.
 17. A process according to claim 14,wherein R₄ and R₅, which are identical or different, are linear orbranched, saturated or unsaturated, aliphatic groups beanng a cyclicsubstituent.
 18. A process according to claim 15, wherein R₄ and R5represent 1 to 3 unsaturated bonds, selected from the group consistingof conjugated double bonds, and triple bonds.
 19. A process according toclaim 14, wherein R₄ and R₅ are linear alkyl groups, branched alkylgroups, alkenyl groups, or alkyldienyl groups.
 20. A process accordingto claim 19, wherein R₄ and R₅ present an hydrocarbon chain which: isinterrupted by an atom or a functional group B selected from the groupconsisting in the groups or atoms of the following formula: —O—, —CO—,—COO—, —OOC—,—OCOO—, —S—, —SO—, —SO₂—,

 wherein R₂ is a hydrogen atom, an alkyl group having 1 to 6 carbonatoms, or a phenyl group, or bears one of the following substituents:—OH, —COR₃, —COOR₂, —CHO, —CN, —NO₂, —CF₃, wherein R₂, which isidentical or different, and R₃, are hydrogen atoms, alkyl groups having1 to 6 carbon atoms, or phenyl groups.
 21. A process according to claim14, wherein R₄ and R₅ are linear or branched halogenoalyl groups having1 to 12 carbon atoms.
 22. A process according to claim 17, wherein R₄and R₅ bear a benzene ring.
 23. A process according to claim 22, whereinan acyclic aliphatic group is bonded to the benzene ring via a covalentbond or by a group B selected from the group consisting in the groups oratoms of the following formula: —O—, —CO—, —COO—, —OOC—, —OCOO—, —S—,—SO—, —SO₂—,

 wherein R₂ is a hydrogen atom, an alkyl group having 1 to 6 carbonatoms, or a phenyl group.
 24. A process according to claim 14, whereinR₄ and R₅ are: monocyclic carbocyclic groups, saturated or having 1 or 2unsaturated bonds in a cycle, the number of carbon atoms in the cyclebeing in the range frorn 3 to 8, or polycyclic carbocyclic groups, thenumber of carbon atoms in a cycle being in the range from 3 to
 8. 25. Aprocess according to claim 14, wherein R₄ and R₅ are benzene rings or aconcatenation of 2 or 3 benzene rings separated by atoms or groups Bselected from the group consisting in the groups or atoms of thefollowing formula: —O—, —CO—, —COO—, —OOC—,—OCOO—, —S—, —SO—, —SO₂—,

 wherein R₂ is a hydrogen atom, an alkyl group having 1 to 6 carbonatoms, or a phenyl group.
 26. A process according to claim 1, whereinthe coupling catalyst is a catalyst comprising at least one metallicelement selected from the 4^(th) and 5^(th) period of groups IIIA, IVA,VA, VIA, VIIA, VIII, IB and IIB of the periodic table.
 27. A processaccording to claim 26, wherein the metallic element is copper, iron,cobalt, nickel, palladium or platinum.
 28. A process according to claim26, wherein the metallic element is supplied in the form of a zerometal, an oxide, an hydroxide, a mineral salt, a cyanide, an oxalate, anacetylacetonate, or an alcoholate.
 29. A process according to claim 26,wherein the metallic element is supplied in the form of a nitrate,sulphate, oxysulphate, halide, oxyhalide, silicate, or carbonate.
 30. Aprocess according to claim 26, wherein the catalyst is copper metal, anorganic copper I compound, an organic copper II compound, an inorganiccopper I compound, or an inorganic copper II compound.
 31. A processaccording to claim 30, the catalyst is selected from the groupconsisting of cuprous bromide, cupric bromide, cuprous iodide, cuprouschloride, cupric chloride, basic copper II carbonate, cuprous nitrate,cupric nitrate. cuprous sulphate, cupric sulphate, cuprous sulphite,cuprous oxide, cuprous acetate, cupric acetate, cuprictrifluoromethylsulphonate, cupric hydroxide, copper I methylate. copperII methylate, and chlorocupric methylate of formula ClCuOCH₃.
 32. Aprocess according to claim 1, wherein the ratio between the number ofmoles of the disulphide compound and the number of moles of thediazonium salt is in the range from 1 to 1.5.
 33. A process according toany one of claim 1, wherein the reaction of the diazonium salt of abiphenyl aromatic compound with the disulphide compound is carried outin an aqueous medium, comprising water, the quantity of water present inthe medium being from 100% to 500% by weight of the biphenyl aromaticcompound.
 34. A process according to claim 1, characterized in whereinthe reaction of the diazonium salt of a biphenyl aromatic compound withthe disulphide compound is carried out in the presence of an organicsolvent.
 35. A process according to claim 34, wherein the solvent isacetic acid.
 36. A process according to claim 1, comprising the steps ofadding the disulphide compound to the diazonium salt, and then addingthe catalyst.
 37. A process according to claim 1, wherein the reactionof the diazonium salt of a biphenyl aromatic compound with thedisulphide compound is carried out at a temperature in the range from 0°C. to 120° C.
 38. A process according to claim 37, wherein thetemperature is in the range from 80° C. to 100° C.
 39. A processaccording to claim 3, wherein the biphenyl aromatic thioether compoundhas the following formula (VI);

R₁ and Z are defined in claim 3, and R₄ is a hydrocarbon group having 1to 24 carbon atoms.
 40. A process according to claim 39, wherein thebiphenyl aromatic thioether compound is4-chloro-4′-thiomethyldiphenylether.